In-tank fuel filters are known in the art, e.g., U.S. Pat. No. 5,902,480. Commercially available in-tank fuel filters known to applicant typically include an outer covering or support layer in the form of a non-woven mesh fabric and one or more layers of filtration material, including one or more layers of spunbonded filaments, melt-blown filaments or needle-punched synthetic fibers.
The in-tank fuel filters disclosed in the above-referenced '480 patent include an extruded, bi-planar mesh covering or support layer and layers of spunbonded filaments and/or melt-blown filaments. One commercially filter disclosed in the '480 patent includes an extruded mesh covering or support layer and internal filtration layers including three layers of Nylon meltblown filaments sandwiched between layers of spunbonded filaments. The three layers of melt blown filaments include outer layers each having a thickness of 17 mils and an intermediate or central layer having a thickness of 15 mils. In this commercial embodiment the meltblown layers provide a gradient filter material; having increased tightness from the outside in. In other words, the pore size is the greatest in the meltblown layer that first encounters the fuel to be filtered; with the pore size decreasing in each, subsequent meltblown layer.
While this latter commercial filter is generally satisfactory for its intended use a need exists for a high efficiency filter structure having improved dust retaining capacity. Such an improved filter structure is capable of removing a desired level of particulates from the fuel over a longer period of time than the above-identified commercial filter structure disclosed in the '480 patent. This prior art structure, which includes only spunbond layers and meltblown layers as the filter components, is sometimes referred to or identified herein as “Prior Art Structure.”
In accordance with an improved prior art structure, the outer layer is the same bi-planar extruded mesh covering or support layer as in the Prior Art Structure and the filter layers include the following, in a direction inwardly from the outer layer: (1) a Nylon spunbonded layer (same as in Prior Art Structure), (2) two layers of Nylon meltblown filaments (same as in Prior Art Structure), (3) a bi-planar extruded mesh being thicker and more open than the covering or support layer, (4) a Nylon meltblown layer (same as in Prior Art Structure) and (5) a Nylon spunbonded layer (same as in Prior Art Structure). In this improved prior art structure the meltblown layer upstream of the bi-planar extruded mesh layer collapses into the pores of the extruded mesh to provide pockets that increase the dust holding capacity relative to the prior art structure that omits the internal, bi-planar extruded mesh layer. This improved structure is sometimes referred to or identified as “Improved Prior Art Structure.”
However, in spite of the relative effectiveness of the Prior Art Structure and the Improved Prior Art Structure, a further improvement in dust holding capacity is desired, without sacrificing filter efficiency. It is to such a filter structure that the present invention relates.
It also has been disclosed to form a fuel filter with one or more layers of fibrillated fibers and employing one or more layers of wet-laid synthetic or organic fibers. For example, see U.S. Publication No. 2014/0224727.
Although filters employing various combinations of fibrillated and non-fibrillated fibers are disclosed in the '727 publication, there is no teaching or suggestion of the structure of the in-tank filters of the present invention and the benefits derived therefrom.
The following additional patents and publications are of general background interest:                U.S. Publication No. 2010/0000411        U.S. Publication No. 2012/0238170        U.S. Publication No. 2013/0092639        U.S. Publication No. 2014/0102974        International Publication WO 2006/135703        U.S. Pat. No. 7,883,562        U.S. Pat. No. 8,608,817        
The above-identified patents and published applications, including the international publication, are fully incorporated by reference herein.